So this might sound like a silly question, but what exactly are the gameplay effects if your colonist has sight 0%? My blind guy can still research and heal, but I haven't tried shooting with him jet.
You basically have very, very chance to hit an enemy with both a ranged and melee weapon. Sight is partially needed for several skills like Cooking, Doctoring and such.
The key word here is 'partially', since it takes other skills in consideration, making it possible for your colonist to be able to cook and butcher, at the cost of speed and efficiency. ^^